fix(playwright-core): bring back index.js in playwright-core (#2691)

References #2540

packages/playwright-core/index.js

@@ -0,0 +1,19 @@
+/**
+ * Copyright (c) Microsoft Corporation.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const { Playwright } = require('./lib/server/playwright');
+
+module.exports = new Playwright(__dirname, require('./browsers.json')['browsers']);